Can't use the camera
My guess is that you accidentally set some other object as your active camera (yes, believe it or not this is possible - Ctrl+Alt+Num 0 snaps the active camera to the view, whereas Ctrl+Num 0 re-assigns the active camera to whatever object you have selected - easy to mix up by mistake). To fix it, select your camera, and then make it the active camera again from the View menu or by pressing Ctrl+Num 0. This should make it behave as normal again: